The overall objective of the project is to increase our understanding of the cause, significance and mechanism of the normally-occurring loss of neurons from the developing nervous system. The trochlear nucleus-nerve-superior oblique muscle system of white Peking duck embryos is used as a model. The role of the peripheral field of innervation in determining whether the nerve cell survives or dies is currently being investigated by peripheral manipulations (such as removal, overloading and blockading neuromuscular transmission).